IST_DATA is a standard SAP Structure so does not store data like a database table does. It can be used to define the fields of other actual tables or to process "IS-T: Telephone Numbers" Information within sap ABAP programs. This is done by declaring abap internal tables, work areas or database tables based on this Structure. These can then be used to store and process the required data appropriately. i.e. DATA: wa_IST_DATA TYPE IST_DATA.
The IST_DATA table consists of various fields, each holding specific information or linking keys about IS-T: Telephone Numbers data available in SAP. These include OBJECT_ID (Additional Reference Object), GROUP_ID (Group Indicator), TNUM_COMP (Complete Telephone Number), COUNTRY_CODE (Country Code)... See below for full list along with technical details, documentation, text table, check tables, foreign key relationships, conversion routines, relevant tcodes and example ABAP select code etc. .